Baltasar Gracian's Aphorism #235: "Know how to ask. With some nothing is easier: with others nothing is so difficult. Some men do not know how to refuse: with them no skill in asking is required. But with others, their first word at all times is "No"; with them great art is required. And with all you should seek the propitious moment. Surprise them when in a pleasant mood, when a repast of body or soul has just left them refreshed, or when their attention does not anticipate the plan of the applicant. The days of joy are the days of favour, for joy overflows from the inner man into the outward creation. It is no use applying when another has been refused, since the patron will have lost all reluctance to say "No." Nor is it a time of sorrow a wise time to ask. To oblige a person beforehand through a conferred favor is a sure way, unless he is a mean person of little self." 
My interpretation: the aphorism is straight forward. I am struck by how the sentiments expressed sound antiquated, however. For example, the suggestion to ask a favor from someone when his "attention does not anticipate the plan of the applicant" seems manipulative to modern ears. And, in some sense, it is. But what is wrong with timing requests in such a manner as to increase the likelihood of a "yes." It is akin to asking for a raise at work in the wake of completing a big project on time and on budget.
Our society values spontaneity over restraint, bluntness/rudeness over tact, indulgence over self-restraint, "going for it" over planning... Arguments can be made for either side but I think the classical virtues win hands-down when it comes to constructing a successful life. And, as with every construction, it is brick by brick, board by board. One piece is knowing how to refuse; another is knowing how to ask. If you construct your character in a conscious manner, then you lay a firm foundation for 'freer' responses, like spontaneity. The situation is akin to an artist learning the mechanisms of perspective before drawing freehand.